Is iOS 10 worth upgrading to and loosing the jailbreak? Also is it worth upgrading from an iPhone 6s plus to 7 plus?

I had a jailbroken iPhone 6S+ and upgraded to the 7+, which meant giving up my jailbreak. I think its definitely worth it to upgrade to the 7+ because of the speed. The 7+ is a beast when it comes to performance and I really enjoy the stability and the new iOS 10 features. I also have an Apple Watch, so the latest Watch OS also works well with it.

Youve got a great set up either way, but the upgrade is definitely worth it.

Is iOS 10 worth upgrading to and loosing the jailbreak? Also is it worth upgrading from an iPhone 6s plus to 7 plus?

I wouldn't, unless the current version is jailbreaked. I'm a die hard iOS freedom lover. The few times I had to use stock iOS before a jailbreak was made available was my iDevices horror experience times.
Back to your topic, i think it completely depend on you, have deep do you depend on cydia tweaks apps? iOS 10 is polished and look beautiful, but personally the jailbreak out weight any stock iOS and 10 is no exception.

Is iOS 10 worth upgrading to and loosing the jailbreak? Also is it worth upgrading from an iPhone 6s plus to 7 plus?

Personally, I have a jailbroken device and it is absolutly amazing. You get to customize your device like no one else can. And even so, you can get many of the iOS 10 feature by downloading a few tweaks such as Floater (Rounded CC), Cream (Coloured Toggles), Watch Notifications (NC + Lockscreen), Auxo (CC Pages), Springtomize/HideMeX (Hide Stock iOS apps), Lock HTML (Lock screen widgets) etc. And also keep in mind that Pangu is working hard on a new jailbreak for iOS 10. In regards to your other question, yes it is worth it to upgrade your iPhone 6s to a 7+ however do keep in mid you will lose your jailbreak as well a some money in your wallet.

I wouldn't. I really like the customization options when you jailbreak. For me it's about workflow and optimization. Stock iOS, even its latest iteration, doesn't offer some must haves for me that are standard on stock Android: mouse support, swiping/gestures, file manager, ability to attach files on emails, landscape mode on a smaller device and the ability to close all open apps. Those are really all the extra features I need and are features that everyone would find useful. It's mind-boggling that Apple hasn't made them standard yet.

I was jailbroken until I got my new iPhone 7+, and the prospect of a possible jailbreak for 10.1 makes this an issue nowadays for people like me.

The issue for me is the balance of the value of the near-perfect stability of standard iOS versus the value of the jailbreak tweaks. My thought is that I really haven’t missed most aspects of jailbreaking except for a few key tweaks. Tweaks like onehandwizard and a few others are genuinely missed, but the stability has been so much better that I don’t know if I’ll jailbreak again.

Don’t get me wrong, I have usually been a strong advocate of jailbreaking and I have purchased a ton of paid tweaks over the years, but with stock iOS I can’t remember the last instability forced restart or any of that nonsense. Plus, as more iOS stock apps have redesigned to make single handed operation of the larger iPhones easier, and cool new features are introduced to stock iOS more rapidly, I’m just not sure if jailbreaking is still worth it for me.

I suppose I’ll just have to see if downgrading from 10.2 to iOS 10.1 in hopes that a new jailbreak comes out soon is something I’m wiling to do...

I was jail broken for many years until I got my iPhone 7. I currently run iOS 10.3.2. There are a few things I miss, but the new iOS incorporated most of the things that I used to have to jailbreak to get. I honestly don't think I'd jailbreak again right now.